The new French prime minister, Manuel Valls, has caused surprise and shock with his choice of ministers to form the country's "combat government".

Among the new appointments were Ségolène Royal, the 2007 presidential candidate and one-time partner of the president, François Hollande, with whom she has four children. She was given the ecology, energy and sustainable development portfolio.

Perhaps the most surprising announcement was the naming of the leftwing Arnaud Montebourg, from the opposite side of the Socialist party to Valls, as economics minister.

Montebourg, who stood as a rival to Valls for the Socialist presidential nomination in 2011 – both lost to Hollande – was nicknamed Monsieur Made in France after urging economic patriotism. His anti-globalisation views, voiced as minister for France's industrial renewal, have been well aired, and he leans towards protectionism.

Another surprise appointment was the inexperienced Benoît Hamon, to the education portfolio. Hamon, who is also on the left wing of the party, has been in government for less than two years, in the relatively junior post of consumer and social economy minister.

Najat Vallaud-Belkacem lost her portfolio as government spokesperson but remains minister for women's rights.

Of the 15 top cabinet posts, seven are now held by women. Valls will hold his first ministerial council on Thursday. The lower secretary of state jobs are expected to be decided next week but Hollande has called for a smaller, tighter and less expensive administration.

Royal's return to frontline politics was made possible by the ending of Hollande's relationship with Valérie Trierweiler in January, for whom he left Royal after it was revealed he was having an affair with a French actor.